Fix ESLint errors in spec/api/plugin-api.spec.js

Fix the following errors:

   59:35  error  "options" is defined but never used  no-unused-vars
   91:11  error  "plugin" is defined but never used   no-unused-vars
  102:35  error  "options" is defined but never used  no-unused-vars
  128:35  error  "options" is defined but never used  no-unused-vars

Note that ESLint revealed a real problem where the test supposedly
verifying receiving options by a plugin didn't actually verify anything.

spec/api/plugin-api.spec.js

@@ -56,7 +56,7 @@ describe("plugin API", function() {
 
     it("receives configuration", function() {
       var plugin = {
-            use: function(config, options) {
+            use: function(config) {
               var i;
 
               expect(config).toBeObject();
@@ -87,19 +87,19 @@ describe("plugin API", function() {
     });
 
     it("receives options", function() {
-      var buildParserOptions = { foo: 42 },
-          plugin             = {
+      var plugin             = {
             use: function(config, options) {
               expect(options).toEqual(buildParserOptions);
             }
-          };
+          },
+          buildParserOptions = { plugins: [plugin], foo: 42 };
 
       PEG.buildParser(grammar, buildParserOptions);
     });
 
     it("can replace parser", function() {
       var plugin = {
-            use: function(config, options) {
+            use: function(config) {
               var parser = PEG.buildParser([
                     'start = .* {',
                     '  return {',
@@ -125,7 +125,7 @@ describe("plugin API", function() {
 
     it("can change compiler passes", function() {
       var plugin = {
-            use: function(config, options) {
+            use: function(config) {
               var pass = function(ast) {
                     ast.code = '({ parse: function() { return 42; } })';
                   };